The present invention relates to an apparatus and method for checking a reflective cone and, more particularly, to such an apparatus and method in which the included angle between opposite sides of the curved surface of the reflective cone are measured.
Reflectors in a conical shape have utility in various optical systems. Such a reflector has a reflective, curved surface which may be used to reflect a beam of light. When the beam is generally aligned with the axis of the cone and directed so as to strike the cone at its apex and on the curved surface surrounding the apex, the beam is reflected radially outward from the axis of the cone. If the included angle between opposite sides of the cone is ninety degrees, the beam is reflected radially outward in a plane. For example, a laser beam may thus be reflected into a plane which provides a continuous reference level over a construction site.
A laser beam transmitted which utilizes a similar conical reflector is shown in U.S. Pat. No. 4,679,937, issued July 14, 1987, to Cain et al, and assigned to the assignee of the present invention. The Cain et al transmitter provides a conical reflector having an included angle which is slightly less than ninety degrees. The laser light beam travels upward, striking the reflector and being reflected into a slightly upwardly directed conical shape. This is more than compensated by refraction of a surrounding glass housing, however, so as to produce a cone of laser light which is directed slightly downward. The purpose of this slight downward tilt to the reference cone of light is to compensate in part for the curvature of the earth over relatively large construction sites.
A principle problem which exists in the production of conical reflectors, regardless of the angle of the apex of such reflectors, is the difficulty in testing the reflectors for conformity to design specifications. This difficulty is due to the curved shape of the surface being measured and to the narrow tolerances to which reflectors must be constructed for some applications. It will be appreciated that if the transmitter using the reflector has an operating range of 1000 feet, even a very small deviation in the angular orientation of the reflective surface produces an appreciable and unacceptable error in the position of the reference light plane at the more remote points of the construction site. While some test fixtures have been developed in the past for testing conical reflectors, such test fixtures have been difficult to set up and time consuming to use.
It is seen that there is a need, therefore, for an apparatus and method for measuring the included angle of a reflective cone between opposite sides of the cone, in which the measurement process can be effected quickly and accurately.